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Electronics Forum / Basics / December 2005White noise generator
I would be grateful for suggestions on constructing a simple random noise generator. Most of the noise should be within the audio spectrum. R >I would be grateful for suggestions on constructing a simple random noise >generator. Most of the noise should be within the audio spectrum. > >R Radio Shack sells a little amplified-speaker box, $9 or something. It's very noisy, and should output a reasonable amount of noise via the headphone jack. I can't vouch for its statistics. The more formal way to do this would be to bias a low-power 10-volt zener to maybe 1 mA current, and amplify that. Figure the zener will make roughly 300 nV/rootHz noise density, or about 40 microvolts RMS in the audio KHz range. You can also make noise digitally, with a pseudo-random shift register. See AoE. John > >I would be grateful for suggestions on constructing a simple random noise > >generator. Most of the noise should be within the audio spectrum. [quoted text clipped - 14 lines] > > John Thanks. Radioshack stuff is unavailable for me. The second option is more in line with what I anticipated. Will one operational amplifier be sufficient? I am not interested in the quality of the noise but merely getting sufficient to drive a small speaker fairly hard. Roger. >> >I would be grateful for suggestions on constructing a simple random noise >> >generator. Most of the noise should be within the audio spectrum. [quoted text clipped - 21 lines] > >Roger. I's suggest two opamps, each with a closed-loop gain of, say 50, to get you up to 100 millivolts RMS, then some sort of power amp to drive the speaker, one of those cheap National thingies maybe. A single opamp might work, ahead of the amp, depending on your numbers... x1000 at 3KHz requires at lease a 3 MHz gain-bandwidth opamp. John > I's suggest two opamps, each with a closed-loop gain of, say 50, to > get you up to 100 millivolts RMS, then some sort of power amp to drive [quoted text clipped - 3 lines] > > John Thanks. Would a 741op-amp drive a small speaker? If so would two or three of these in series do the job? Would you bias the + input to half the single supply voltage (12 volts) in each case and use 470pf capacitors between the zener diode and the first stage, between each stage and between the last stage and the speaker? Roger >> >"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in > message [quoted text clipped - 9 lines] > > Thanks. Would a 741op-amp drive a small speaker? if your small speaker has an impedance of 50 or more ohms and ypu don't need it very loud it could work. an LM386 is a better choice for a small 4 or 8 ohm speaker. Bye. Jasen John Larkin wrote: > >I would be grateful for suggestions on constructing a simple random noise > >generator. Most of the noise should be within the audio spectrum. [quoted text clipped - 9 lines] > make roughly 300 nV/rootHz noise density, or about 40 microvolts RMS > in the audio KHz range. Don't semiconductor junctions make excess shot noise though ? > You can also make noise digitally, with a pseudo-random shift > register. See AoE. Nat Semi once made a chip that did that. I have a 'little box' I made using one. Sounds horrid. You can hear the pattern. Graham p.s. I've sometimes heard shot noise referred to a Schott noise. Any idea which is correct ? >John Larkin wrote: > [quoted text clipped - 13 lines] > >Don't semiconductor junctions make excess shot noise though ? At this sort of current, zeners are pretty white and gaussian, maybe just a tad asymmetric. At much lower currents, shot noise is significant. >> You can also make noise digitally, with a pseudo-random shift >> register. See AoE. > > Nat Semi once made a chip that did that. I have a 'little box' I made using >one. Sounds horrid. You can hear the pattern. The sequence must have been short. A 1 MHz, 64-bit shift register won't repeat in your lifetime. >Graham > >p.s. I've sometimes heard shot noise referred to a Schott noise. Any idea >which is correct ? I think it's "shot", like buckshot falling on the roof. John > I would be grateful for suggestions on constructing a simple random noise > generator. Most of the noise should be within the audio spectrum. Tune a cheap FM radio inbetween stations. > > I would be grateful for suggestions on constructing a simple random noise > > generator. Most of the noise should be within the audio spectrum. > > Tune a cheap FM radio in between stations. The cheapest FM radio would still need an amplifier as the speaker has to be well separated from the signal generator in the application that I have in mind. R >> Tune a cheap FM radio in between stations. > > The cheapest FM radio would still need an amplifier as the speaker has to > be well separated from the signal generator in the application that I have > in mind. It would help if you described your application. (The PP was referring to using an FM radio with NO signal) Since you mention a speaker, do you really need white noise, or just some "noise"? > >> Tune a cheap FM radio in between stations. > > [quoted text clipped - 7 lines] > Since you mention a speaker, do you really need white noise, or just some > "noise"? Noise across the audio spectrum of a small speaker. The speaker will be some metres away from the signal generating part of the device. The noise level must be controllable nearly upto the limit of the speaker. I have just about come around to the idea of a 12 volt Zener diode driving two LM741s followed by a LM368N to drive the speaker. The op-amps would have a 12 volt unbalanced supply with the + inputs of the LM741s biassed to 6 volts. The parts are all available and cheap. I have the speaker. Would this work in your view? R >> >> Tune a cheap FM radio in between stations. >> > [quoted text clipped - 21 lines] > >R You can't really zener a 12-volt zener from a 12-volt supply. And 741's are notoriously noisy themselves, which can cut both ways. John > >> Since you mention a speaker, do you really need white noise, or just some > >> "noise"? [quoted text clipped - 16 lines] > > John Thanks. Should I use a lower voltage zener diode then? The extra noise will not matter. Roger >> >> Since you mention a speaker, do you really need white noise, or just >some [quoted text clipped - 26 lines] > >Roger If you use a 6-ish volt zener, it can be the supply splitter, too! John > >> >> Since you mention a speaker, do you really need white noise, or just > >some [quoted text clipped - 30 lines] > > John Connect the + input directly to ground and feed the signal through a (?)100 nF capacitor and a resistor into the - input? Roger >> >"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in >message [quoted text clipped - 42 lines] > >Roger See my sketch in a.b.s.e. John > >> >"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in > >message [quoted text clipped - 6 lines] > > See my sketch in a.b.s.e. My ISP does not provide a.b.s.e which I presume is a binary ng covering electronics. I would be very grateful if you could manage to email me the drawing as a .jpg file. Roger >> See my sketch in a.b.s.e. > > My ISP does not provide a.b.s.e which I presume is a binary ng covering > electronics. it is. "alt.binaries.schematics.electronics". (note to self:"Avoid IHUG") fwiw Clear and compass/freenet carry it. compass/freenet's server is half-arsed. AFAIK there's me and maybe two other people who actually use it.  SignatureBye. Jasen > I would be grateful for suggestions on constructing a simple random noise > generator. Most of the noise should be within the audio spectrum. I use a 10 Megohm resistor and amplify the f**k out of it with a low noise op-amp. Graham Any reverse biased eb junction is noisy like a zener diode. This is white noise... equal energy per hz... you want pink noise? (equal energy per octave) >> I would be grateful for suggestions on constructing a simple random noise >> generator. Most of the noise should be within the audio spectrum. [quoted text clipped - 3 lines] > >Graham The opamp noise would probably wind up dominating the resistor noise. That might be OK, but opamp noise tends to be fairly non-white, with a lot of excess low-frequency (1/f) component and occasional pops and other weirdness. John John Larkin wrote: > >> I would be grateful for suggestions on constructing a simple random noise > >> generator. Most of the noise should be within the audio spectrum. [quoted text clipped - 10 lines] > > John I make 10 Meg = 409 nV / sqrt Hz Used with a TL07x type op-amp ( 12 nV / sqrt Hz ) it seems to be just fine. With a bipolar op-amp you would indeed likely get loads of input current related noise though. Graham >John Larkin wrote: > [quoted text clipped - 21 lines] > >Graham Yeah, that works. What's the input capacitance on one of those? John John Larkin wrote: > >John Larkin wrote: > > [quoted text clipped - 25 lines] > > John Seems to be unspecified. I know what you're thinking. I've used that configuration for test jigs - can't recall now if I did a sweep across the audio spectrum. JFET input btw. Graham >I would be grateful for suggestions on constructing a simple random noise > generator. Most of the noise should be within the audio spectrum. > > R Check out http://www.discovercircuits.com/N/noisegen.htm Also go to Google and put it "white noise circuits", there is a lot of good information there. Brian > >I would be grateful for suggestions on constructing a simple random noise > > generator. Most of the noise should be within the audio spectrum. > > R > Check out http://www.discovercircuits.com/N/noisegen.htm Also go to Google > and put it "white noise circuits", there is a lot of good information there. > > Brian I used a circuit I found that used a saturated transistor few parts and a 9 V. Very simple and I put it into the mike input of a portable radio. Worked great as a noise blanker for the babies room. Richard >I would be grateful for suggestions on constructing a simple random noise >generator. Most of the noise should be within the audio spectrum. You might want to check out my DaqGen freeware at www.daqarta.com. It uses the sound card on any Windows computer and can generate all sorts of test signals, including non-repeating white and pink noise as well as band-limited noise. You can see the real-time waveform or spectrum of the noise, average to see flatness over time. or run a histogram to get the amplitude distribution. Best regards, Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis www.daqarta.com Home of DaqGen, the FREEWARE signal generator > I would be grateful for suggestions on constructing a simple random noise > generator. Most of the noise should be within the audio spectrum. > > R Record one of Howard Deans' speeches/rants. That's some pretty good white noise. >> I would be grateful for suggestions on constructing a simple random noise >> generator. Most of the noise should be within the audio spectrum. [quoted text clipped - 3 lines] >Record one of Howard Deans' speeches/rants. >That's some pretty good white noise. Pink noise, actually. John > >> I would be grateful for suggestions on constructing a simple random noise > >> generator. Most of the noise should be within the audio spectrum. [quoted text clipped - 7 lines] > > John LOL, yeah, you're right. Maybe even a bit red. > > I would be grateful for suggestions on constructing a simple random noise > > generator. Most of the noise should be within the audio spectrum. [quoted text clipped - 3 lines] > Record one of Howard Deans' speeches/rants. > That's some pretty good white noise. That fellow, whoever he may be, is of so little interest to anyone in this country (NZ) that his rants are unavailable and unrecorded. R |
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